Comparing Ray Trace and Fk-Modeling of the Refracted Wave Associated with Normal Mode

Abstract

An acoustic wave traveling through the water layer will, upon hitting the seafloor at the critical angle, generate a head wave traveling in the upper part of thesubsurface. While some of the energy is converted to this first head wave, some isreflected back to the sea surface only to reflect back to the sea floor again at criticalangle, creating multiple head waves. This collection of head waves will travel at agreater speed than the direct wave in the water layer, and will therefore be recordedfirst at a receiver at large enough offset. This refracted wave is the first part of whatis called the normal wave mode.

In this thesis, an equation proposed by M. Landrø and L. Amundsen, which has yet to be tested against synthetic modeling, is modeled in Matlab using ray tracing theory. Synthetic traces are created using the Osiris software, and the traces from the two models are compared to ascertain the validity of the equation. It is shown that the Matlab model successfully recreates the refracted wave and compares very well to the modeling done in the Osiris software. It is also shown how the reflection coefficient at the sea surface can influence the amplitudes, and how the refracted waves get attenuated as the water depth increases.